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BENGALURU, April 26, 2026 -- A traffic study that the Bangalore Development Authority (BDA) hoped would settle the debate over the Hebbal short tunnel has instead opened a new front. IISc researchers and a former top transport planner are dismissing the IIT-Bombay professor's report as methodologically weak, based on outdated data, and unable to prove the tunnel is needed.
The study, titled "Integrated Traffic Microsimulation Study – Bengaluru: Hebbal Flyover & Hebbal Short Tunnel," was prepared by Prof Archak Mittal for Rithwik Projects Private Limited. BDA commissioned it after the short tunnel faced sustained public criticism. The agency's senior officials now point to the study as a validation of the project. But a closer look by reviewers paints a very different picture.
Prof Ashish Verma, who heads the Sustainable Transportation Lab at IISc, reviewed the report and found a basic contradiction at the heart of the model. For the 2027 peak-hour base case, the IIT-Bombay study shows an average speed of 13.74 kmph. The DPR for the Hebbal short tunnel—the document from which the study takes its traffic data—had used a far lower figure of 4.29 kmph. A three-fold difference in the assumed base condition should be impossible to overlook.
Verma's review also notes that the study does not report queue lengths before and after the proposed interventions. Queue length is a direct indicator of how badly an intersection or underpass is performing. Without it, the claimed decongestion benefit of the tunnel cannot be verified. Verma adds that the study's methodology is not described in sufficient detail for an outside expert to reproduce the results.
The design problem Verma highlights is even more fundamental. The proposed elevated corridor at Mehkri Circle has no ramp for vehicles moving straight towards Windsor Manor. Only traffic turning from Mehkri Circle would be able to use the flyover. A large share of vehicles travelling straight would remain on the existing underpass. That sharply limits the corridor's usefulness.
Verma also questioned whether the Mehkri Circle elevated corridor can work alongside the larger east-west corridor proposed between Yeshwanthpur and KR Puram. "There was no clarity on how traffic would be handled on existing roads after the proposed projects shift congestion, or how the projects would be integrated," he told TOI. He said the environmental impact of shifting traffic from one corridor to another should also have been assessed.
Satyajit Arikutharam, former chief technical adviser to the Directorate of Urban Land Transport (DULT), reviewed the same study and did not mince words. He called it "extremely poor quality" and said it repeats the shortcomings of the original DPRs rather than fixing them.
His first complaint concerns the scenario matrix. The study was expected to model four cases: the base case, the tunnel only, the elevated corridor only, and both together. It modelled only two: the base case and the combined tunnel-plus-elevated-corridor option. As a result, the marginal benefit of the short tunnel on its own—the very question BDA asked the study to answer—is never actually analysed.
Arikutharam also points out that the traffic data in the DPR is stale. The Hebbal flyover gained an additional ramp in January 2026, changing the traffic pattern at the junction. The DPR's counts were done before that. "The traffic situation has changed since then," he said. Without fresh volume counts, he argued, no credible conclusion can be drawn about the tunnel's necessity.
The conversion factors used in the study are another major point of dispute. Both the DPRs and the IIT-Bombay study rely on Passenger Car Unit (PCU) factors from the 1990s. Under those old factors, a two-wheeler is given more road-space equivalence than the current Indian Roads Congress guidelines suggest. Arikutharam estimates that this alone could overstate two-wheelers' contribution to congestion by roughly 30%. In a city where two-wheelers form a huge share of traffic, that is not a minor technicality.
The absence of an origin-destination (OD) survey is, in Arikutharam's view, the study's most basic flaw. The IIT-Bombay report itself acknowledges that neither DPR contains an OD study. An OD survey identifies where trips begin and end; without it, there is no way to know whether vehicles moving through Hebbal are local trips, airport-bound trips, or long-distance freight movement. That information is critical for deciding whether a short tunnel, an elevated corridor, or a different set of interventions would actually help.
He also notes two omissions that could change the traffic forecast completely. The study does not account for the proposed metro line in the area, nor for a separate long tunnel project that has been discussed for Bengaluru. The long tunnel, in particular, could pull traffic away from the Hebbal corridor, while the metro could suppress a portion of private-vehicle trips. Ignoring both makes the projections unrealistic.
The report has an internal recommendation that would itself force design changes: it says the distance between the elevated corridor and the tunnel should be increased from 80 metres to 250 metres for smoother traffic movement. If BDA accepts that recommendation, the current project design will have to be redone. If it rejects it, it has to explain why.
A senior BDA official told TOI that the study was commissioned after public anger over the tunnel. "There was a lot of negative publicity and outcry against the short tunnel road, so we decided to go for another third-party institutional evaluation," the official said.
The official described the study as a positive report, saying it found that the tunnel and the elevated corridor are "very much required" for future traffic. He said the short tunnel is expected to be completed by the end of January 2028.
The Hebbal project has now become a strange case of institutional disagreement. BDA invited one academic brand to confer legitimacy on the project. Another academic brand, IISc, has now pulled that legitimacy apart. Add a former DULT adviser with direct experience in Bengaluru's transport planning, and what remains is a report that supports a pre-determined conclusion but cannot withstand professional scrutiny.
None of the critics is arguing that Hebbal does not need better infrastructure. The argument is narrower and more technical: the evidence used to justify the short tunnel is not reliable. The data is old, the scenario analysis is incomplete, the design does not serve the traffic it claims to serve, and the surrounding projects that could change traffic have been ignored.
If BDA proceeds on the basis of this study alone, the project will remain vulnerable to legal challenge and public distrust. The more durable path would be to release the model inputs, commission a fresh origin-destination survey, and re-run the four scenarios with current data. Without that, the Hebbal short tunnel will carry not only traffic but also a heavy burden of unresolved questions.
